Image pickup tube with a mesh electrode supported by a ring



June 13, 19? KOHEl FUNAHASHl ET Al. 3,325,672

IMAGE PICKUP TUBE WITH A MESH ELECTRODE SUPPORTED BY A RING Filed April 15, 1964 INVENTORS KOHEI FUNAHASHI mmmwa mmi TADAO CHUJO United States Patent 3,325,672 IMAGE PECKUP TUBE WHTH A MESH ELECTIRQDE SUPPORTED BY A RlNG Kohei Funahashi, Yokohama-sin, and Tadao Chujo, Tokyo, Japan, assignors to Tokyo Shibaura Electric Co.,

Ltd., Kawasaki-shi, Japan, a corporation of Japan Filed Apr. 15, 1964, Ser. No. 359,877 Claims priority, application Japan, Apr. 22, 1963, Cad/20,161, 38/293622, 33/29,341 Claims. (Cl. 315-l0) This present invention relates to a television image pickup tube and more particularly to an image pickup tube comprising an evacuated tubular envelope, a target contained in said envelope for transforming optical images into electric charge images and an electron gun to produce an electron beam adapted to scan the surface of said target through a mesh electrode disposed adjacent to and in parallel with said target to discharge said electric charge images whereby to drive out signals.

Image pickup tubes of the vidicon type are known in the art as the typical tube of the type mentioned, wherein a transparent conductive signal plate coated with a photo conductive layer is employed as the target to transform the projected optical images into electric charge images. To derive out the electric charge images as the image signals the tube is constructed such that the surface of the target is scanned by an electron beam at each cycle of television frame to discharge the electron charge images whereby to derive out modulated discharge currents from the signal plate. Subsequent to the discharge of positive charge images by means of each scanning by the electron beam, since optical images are projected upon the target, images of positive charges are reformed to be converted into image signals by the electron beam scanning during the subsequent frame period. Electrons emitted from an electron gun disposed in coaxial relation with the tube are sufficiently focussed by the focussing electrode system of the electron gun to form an electron beam directed to the center of the target. In order to scan the target electrostatic deflecting electrodes are included in the focussing electrode system or an electromagnetic deflecting system is disposed on the outside of the tube. After deflection the electron beam is bent in a direction at an angle with respect to the axis of the tube to reach a mesh electrode. The mesh electrode serves to form a decelerating field in a space between it and the target and also to correct the electron beam having a component which is orthogonal to the axis causing the beam to impinge at right angles upon the surface of the target. The mesh electrode is supported integrally, not only electrically but also mechanically, by one end surface of the focussing electrode of the electron gun, adjacent to and in parallel with the target. With the mesh electrode of the construction above mentioned, however, it is impossible to perfectly correct the electron beam having radial component caused by deflection thus forming undesirable shading in image signals. In order to eliminate this difficulty it has been proposed heretobefore to electrical insulate from each other the mesh electrode and the electron gun so as to impress difi'erent potentials to them, and has succeeded to greatly reduce the shading effect. More particularly, the mesh electrode is secured between the target and one end of the focussing electrode constituting the electron gun electrically insulated from and mechanically integral with said end facing the target. The mesh electrode is supported by an annular supporting member which serves also to support an insulator for the mesh electrode. This supporting member has substantially the same diameter as the focussing electrode or is constructed to have a large diameter for the purpose of supporting said insulator which is secured to the outer periphery of the maximum diameter portion of the focussing electrode.

Such a supporting construction of the mesh electrod: is effective to reduce the size of the supporting ring mem her at least to that comparable with the focussing elec trode but the diameter of the focussing electrode is re duced at least by the thickness of the insulator with re spect to the internal diameter of the tubular envelopi because the insulating ring is projected beyond the cute periphery of the maximum diameter portion of the focus sing electrode. As a result the space within the focussin electrode having uniform electric field is reduced. Thus the electron beam would not be subjected to the action 0 uniform field whereby to increase deflection distortion Especially, in an image pickup tube wherein the electro static deflecting system is assembled therein it become impossible to dispose large deflecting plates within focus sing electrodes thus not only increasing undesirable dis tortions of picture and deflection but also decreasing reso lution. Moreover focussing electrode clamps the insulat ing ring by means of a flange welded to the periphera portion of the focussing electrode and the supportin member and the insulating ring are secured together b a supporting means similar to that for the focussing elec trode. Thus the prior art tubes have complicated con struction and are difficult to fabricate.

Thus principal object of this invention is to provide an improved image pickup tube having improved deflectioi distortion.

Another object of this invention is to provide an imagi pickup tube wherein picture distortion is decreased am resolution is increased.

A further object of this invention is to provide a nove image pickup tube having a simplified supporting struc ture for its mesh electrode.

A still further object of this invention is to provide an image pickup tube having a novel supporting structur for its mesh electrode which is easy to fabricate.

These and other objects and advantages of this inven tion, and its various features will appear more fully upoi consideration of the specific embodiments now to be de scribed in detail in connection with the accompanyin drawings, in which:

FIG. 1 shows a schematic sectional view of one em bodiment of thi invention;

FIG. 2 shows an exploded perspective view of impor tant elements of the embodiment shown in FIG. 1;

FIG. 3 shows a sectional view of a modification of thi invention; and

FIG. 4 shows a diagrammatic view to explain the prin ciple of this invention.

Referring now to FIG. 1 of the accompanying drawin there is shown a vidicon type image pickup tube 10 com prising a tubular glass envelope H with one end surfac made of a transparent plate or disc 12 which is ground it have optical flatness. On the inner surface of the end plat 12 is applied a transparent conductive film 14 which i formed by coating means to act as a signal plate. A laye 15 of photo conductive material is applied on the film 1 to complete a target 13. The target is disposed to be in] pinged upon by optical images passing through the trans parent plate 12 and an optical system, not shown, to forr positive electron charge images corresponding to the con trast of the optical images. The electric charge images ar discharged through scanning by an electron beam. Th discharge current is collected by the transparent conduc tive film and is then derived out to a target ring 1 through an indium metal seal 16 adapted to cold seal th transparent plate 12 to the end of the envelope.

The electron beam is produced by an electron gun 1 disposed in the other end of the envelope. The electro. gun comprises a cathode 21 heated by a filament Z9,

rst and a second grid electrodes 22 and 23 to contrc and shape electrons emitted from the cathode into bean form, a first focussing electrode 24, a second focussing electrode and a third focussing electrode 26, each in the form of a metal cylinder and serves to electrostatically focus the electron beam. Among various electrodes the third focussing electrode 26 is positioned nearest to the target and is provided with a large diameter portion comparable with the inner diameter of the envelope. All of the focussing electrodes are held with predetermined spacing therebetween by means of a plurality of glass or ceramic insulating rods which are parallel to the longitudinal axis of the tube. Within the large diameter portion of the third focussing electrode are disposed horizontal deflecting electrodes 28, which are nearest to the cathode, and vertical deflecting electrodes 29, each comprising a pair of deflecting plates and serving to deflect the electron beam so as to cause it to scan across the target. These deflecting electrodes are supported by the insulating rods extending into the focussing electrodes. An insulating ring securing member 31 is secured to the inner surface of the third focussing electrode 21 adjacent to its end facing to the target to secure an insulating ring or cylinder 30. On the opposite end of the cylinder is mounted an annular holder 32 for the mesh electrode 33 comprising a supporting ring 34 and a fine mesh 35 mounted thereon under tension. The electrode 33 is secured to the holder 32 by inserting its supporting ring 34 into the holder with a spacer 36 clamped therebetween.

The structure for supporting the mesh electrode will be described in more detail by referring to FIG. 2. The insulating ring securing member 31, which is adapted to be mounted in the third focussing electrode 26 is made of a metal ring having oppositely extending flanges 41 and 42 on its outer and inner peripheral edges, the size of the ring sufficiently large to be snugly fit in the third focussing electrode. The mesh electrode securing member 32 is also made of metal ring having a cylindrical flange 43 on its inner edge and a notched flaring flange 44 on its outer edge. The flaring flange 44 resiliently engages against the inner wall of the main cylindrical portion of the envelope to coaxially fix the electron gun and also to prevent it from mechanically vibrating. The insulating ring 30 is made of an insulator such as glass or ceramic and is provided with a number of perforations 45 and 46 (four, for example) adjacent to the respective ends thereof. After mounting the securing members 31 and 32 won the insulating cylinder with their inner flanges inserted therein, metal pins 47 and 48 are inserted in the perforations 45 and 46, respectively and fixed by welding. Ihese metal pins ensure very accurate and firm securing. The sub-assembly obtained is then inserted in the third Focussing electrode 26 with the securing member 31 innernost, and is then secured in position by welding the flange 11 of the securing member 31 to the inner wall of one end 3f the third focussing electrode.

As pointed out previously the mesh electrode 33 is iormed by mounting under tension a fine mesh 35 upon 1 supporting ring 34 having a size sufiicient to be resiliently it into the inner flange 43 of the securing member 32. The inner end of the cylindrical flange 34 is slightly vapered for easy insertion while the outer end is formed with a radial flange 49 which serves as the support for the nesh 35 and also as a stopper to limit the extent of inserion. A barrier spacer 36 made of a metal ring is clamped vetween the outer end surface of the securing member 32 1nd the radial flange 49 of the mesh electrode to engage he interior surface of the envelope to prevent foreign Jarticles from depositing upon the target which come from he electron gun side.

It is preferable to fit the mesh electrode 33 in said securng member immediately prior to the sealing step of the :nvelope. Thus, when various electrodes are assembled lftCl' the mesh electrode 33 has been secured, minute care thould be taken to protect the mesh 35 against deposition Jf foreign particles or mechanical damage. Thus it is very 4. advantageous to the fabrication of the tube to mount the mesh electrode in a later step.

To fabricate the image pickup tube various components of the glass envelope 11 including the transparent plate 12, the main tube portion Stl, and a stem 52 having sealed therein a plurality of connecting pins 51 are prepared separately. Thereafter, various electrodes of the electron gun 19 and the deflecting electrodes 28 and 29 are mounted upon the insulating rods 27 with a required spacing therebetween, and the resulted electrode assembly is secured to the connecting pins of the stem 52. Finally, one end of the main tube portion 50 is sealed to the stem 52 by fusion.

The target 13 is formed on the inner surface of the transparent plate 12 in a manner described above and the open end of the main tube portion 50 and the transparent plate 12 are jointed together to seal the tube by means of a suitable cold sealing means such as an indium alloy and the like during evacuation process. Various electrodes are then subjected to baking treatment, and after thorough evacuation an evacuating tube 53 is sealed off to complete the tube.

With the above described construction, it is possible to make the cylindrical third focussing electrode 26 to have its large diameter portion 26 large enough to nearly reach the inner wall of the tube. As a result the region within the electrode wherein the electric field is uniform can be increased to improve the focussing effect upon the electron beam. Further where a deflecting system is located within the electrode it is able to make it to have large size thus decreasing undesirable distortions of picture and deflection.

To illustrate the operating potentials of the tube shown in FIG. 1, the cathode 21 is impressed with zero volt, the target 30 v., the first grid electrode 60 v., the second grid electrode 300 v., the first focussing electrode 200 v., the second focussing electrode from zero to 60 v., the third focussing electrode 200 v. and the mesh electrode 350 v., respectively, from a source of DC supply 60.

The operating of the tube embodying this invention is the same as the electrostatic focussing and electrostatic deflecting type image pickup tube of the prior art. According to this invention, however, since a mesh electrode 33 having a supporting ring 34 having smaller diameter than the maximum diameter portion of the third focussing electrode 26 is utilized, it is able to greatly reduce the shading efiect thereof when compared with conventional construction wherein the ring for supporting the mesh electrode has the same or larger diameter than the focussing electrode. Thus as diagrammatically shown in FIG. 4 the accelerating electric field produced by applying a higher potential to the mesh electrode 33 than the third focussing electrode 26 forms a kind of electrostatic lens as shown by dotted lines and further by reducing the diameter of the inner end of the supporting ring 34 to extend into the focussing electrode it is possible to create a field distribution most suitable to correct the electron beam 56 which has been deflected by the deflecting electrodes. When compared with the above described conventional tube it is more easy to cause the electron beam to impinge at right angles upon the target, thus further decreasing shading.

Also by strengthening the electric field between the mesh electrode and then focussing electrode it is possible to make more powerful the main electrostatic lens formed by the first, second and third focussing electrodes when compared with the construction which does not utilize the accelerating field, thus decreasing the diameter of beam spot. The accelerating field is also effective to decrease the angle of diffusion of the electron beam when it has passed through the mesh electrode. Since reduction of the diffusion angle is effective to decrease the astimagation of the electron beam caused by the decelerating field formed between the mesh electrode and the target, whereby contributes to further decrease in the,

diameter of the focussed beam thus improving the resolution of the image pickup tube. According to this invention it is possible to increase the electric field intensity and hence provide the above function to the maximum extent when compared with the prior art tube wherein the focussing electrode and the supporting ring for the mesh have the same diameter.

Referring now to FIG. 3 illustrating a modification of this invention, the open end 61 of the third focussing electrode 26 in the form of a metal cyclinder has a reduced diameter to be inserted in an insulating ring or cylinder 30. The insulator ring 30 is fixed by inserting metal pins 60 in perforations 62 through the wall of the ring 30 and welding these pins to the outer wall of the open end 61 of the third focussing electrode, in the same manner as in FIG. 1, it being understood that like parts being designated by the same reference numerals.

With this modified construction the open end 61 of the focusing electrode 26 is utilized as the member 31 for securing the insulating ring, shown in FIG. 1, thus simplifying fabrication. In this case the outer diameter of the insulating cylinder 30 is made substantially equal to or smaller than that of the focussing electrode 26.

As has been pointed out in the foregoing embodiments of this invention, the open end of the third focussing electrode facing to the target is made to have smaller diameter than its maximum diameter portion, the reduced open end is utilized to receive an insulating ring so as to secure it, and a mesh electrode having a diameter smaller than the maximum diameter portion of the focussing electrode is inserted and fixed in the opposite end of said insulating ring. This construction permits to dispose the maximum diameter portion of the focussing electrode more closer to the inner wall of the tube which is not only effective to increase the effective space within the tube in which the electron beam travels but also to minimize the distortion of the electron beam. If it is desired to dispose a deflecting electrode system inside the focussing electrode this construction permits use of larger deflecting plates thus decreasing distortions of the picture and deflection while at the same time increasing the resolution.

Although according to this invention the diameter of the open end of the focussing electrode is reduced by an amount corresponding to the thickness of the insulating ring, such reduction has no appreciable effect upon the operating characteristics of the tube.

Method of securing the insulating ring to the focussing electrode by means of metal pins greatly simplifies the fabrication steps of the tube and also contributes to simplify the construction of the supporting means for the mesh electrode.

While in the foregoing description this invention has been explained by referring to image pickup tubes of the electrostatic deflecting and focussing type it should be understood to those skilled in the art that the invention can equally be embodied in the image pickup tubes of the electromagnetic deflecting and focussing type and that various changes and modifications can be made Without departing from the true spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An image pickup tube comprising an evacuated tubular envelope, a target disposed in said envelope at one end thereof, a mesh electrode disposed adjacent to and in parallel with said target, said mesh electrode having a mesh supporting ring on the side thereof opposite to that facing to said target, an electron gun disposed in the 0pposite end of said envelope coaxially therewith to emit an electron beam which is adapted to scan said target, said electron gun having a cylindrical focussing electrode on the side thereof facing to said target, and an insulatii cylinder having smaller internal diameter than the ma imum diameter portion of said focussing electrode, or end of said insulating cylinder being fixed to the op end of said focussing electrode facing to said targ whereas the other end of said insulating cylinder beii adapted to receive and insulatedly support said supporti1 ring of said mesh electrode.

2. The image pickup tube according to claim 1, where electrostatic deflecting electrodes are disposed in sa focussing electrode.

3. An image pickup tube comprising an evacuatt tubular envelope, a target disposed in one end of sa envelope, a mesh electrode disposed adjacent to and parallel with said target, said mes-h electrode having mesh supporting ring on the side thereof opposite to th facing to said target, an electron gun disposed in the o posite end of said envelope coaxially therewith to em an electron beam which is adapted to scan said target, sa electron gun having a cylindrical focussing electrode the side thereof facing to said target, an insulating rin means to secure said insulating ring to the internal we of said focussing electrode adjacent the open end there facing to said target, and means to secure said mesh ele trode, said insulating ring having an external diamet smaller than the maximum diameter portion of said focu sing electrode, one end of said insulating ring being so ported by said securing means whereas the other end b ing adapted to receive said mesh electrode securing mea] which is electrically insulated from said focussing ele trode, said mesh electrode securing means being adapte to receive said supporting ring of said mesh electrode 5 as to conductively support it.

4. An image pickup tube comprising an evacuate tubular envelope, a target disposed in one end thereof, mesh electrode disposed adjacent to and in parallel wi' said target, said mesh electrode having a mesh supportir ring on the side thereof opposite to that facing to sa target, an electron gun disposed in the opposite end i said envelope to emit an electron beam which is adaptc to scan said target, said electron gun having a cylindric focussing electrode on the side thereof facing to sa target, an insulating ring, means mounted on the inn wall of said focussing electrode adjacent the open er thereof to secure said insulating ring, said insulating ri1 having a plurality of perforations adjacent the opposi ends thereof, means including metal pins inserted in sa porforations adjacent one end to secure said insulatir ring to said securing means, one end of each of said pi being welded to the wall of said securing means, mea including second metal pins inserted in the remaini: perforations to secure said insulating cylinder to said me electrode securing means, one end of each of said secoi metal pins being welded to the wall of said mesh 61361104 securing means, said supporting ring of said mesh ele trode being inserted in said mesh electrode securing mea to be electrically supported thereby.

5. The image pickup tube according to claim 1 where said mesh electrode is maintained at a higher potenti than said focussing electrode to form an electrostatic 1e of an accelerating field between said electrodes.

References Cited UNITED STATES PATENTS 3,069,586 12/1962 Antoniades 31365 JOHN W. CALDWELL, Acting Primary Examiner.

T. A. GALLAGHER, Assistant Examiner. 

1. AN IMAGE PICKUP TUBE COMPRISING AN EVACUATED TUBULAR ENVELOPE, A TARGET DISPOSED IN SAID ENVELOPE AT ONE END THEREOF, A MESH ELECTRODE DISPOSED ADJACENT TO AND IN PARALLEL WITH SAID TARGET, SAID MESH ELECTRODE HAVING A MESH SUPPORTING RING ON THE SAID THEREOF OPPOSITE TO THAT FACING TO SAID TARGET, AN ELECTRON GUN DISPOSED IN THE OPPOSITE END OF SAID ENVELOPE COAXIALLY THEREWITH TO EMIT AN ELECTRON BEAM WHICH IS ADAPTED TO SCAN SAID TARGET, SAID ELECTRON GUN HAVING A CYLINDRICAL FOCUSSING ELECTRODE ON THE SIDE THEREOF FACING TO SAID TARGET, AND AN INSULATING CYLINDER HAVING SMALLAR INTERNAL DIAMETER THAN THE MAXIMUM DIAMETER PORTION OF SAID FOCUSSING ELECTRODE, ONE END OF SAID INSULATING CYLINDER BEING FIXED TO THE OPEN END OF SAID FOCUSSING ELECTRODE FACING TO SAID TARGET WHEREAS THE OTHER END OF SAID INSULATING CYLINDER BEING ADAPTED TO RECEIVE AND INSULATEDLY SUPPORT SAID SUPPORTING RING OF SAID MESH ELECTRODE. 